CAIRO—Egypt's powerful top general asked Egyptians to protest on Friday to support the military's right to confront supporters of ousted President Mohammed Morsi, an appeal that Mr. Morsi's backers said amounted to a prelude to civil war.

Hours later, the U.S. sounded its most emphatic concerns yet over the country's political deterioration, saying it would suspend a planned delivery of F-16 fighter jets to Egypt's military.